The present invention relates generally to systems and methods for direct fabrication of micro- and macro-scale objects in a vacuum. More specifically, the present invention pertains to systems and methods for precisely directing metallic and ceramic powders for deposition on a substrate to form micro- and macro-scale objects in a vacuum.
In co-pending PCT Patent Application Serial No. PCT/US01/12952, filed on Apr. 20, 2001 designating the United States and entitled xe2x80x9cMethod and System for Thick-Film Deposition of Ceramic Materialsxe2x80x9d (hereinafter the xe2x80x9cPCT Applicationxe2x80x9d), a system and method for fabricating micro- and macro-scale objects in air is disclosed. In brief the system described in the PCT Application propels metal or ceramic particles toward a substrate, melts the particles using a laser beam to form liquid droplets as the particles travel toward the substrate, and undercools the droplets before they impact the substrate. The undercooling of the droplets is critical to the formation of films and objects having desired properties. The undercooling is a function of the temperature of the droplets and the distance between the substrate and the point where the particles exit the laser beam, i.e., the working distance. The undercooling is also a function of the size and the particles. The PCT Application is hereby incorporated by reference in its entirety.
Fabricating micro-and macro scale objects in air using the system described in the PCT Application, however, presents problems. First, contaminants, such as oxygen or nitrogen, in the air come into contact with the liquid droplets, affecting the properties of the resulting film or object. Second, the size of particles used with the system is limited by the fact that the liquid droplets are subject to Is conduction cooling in the air. As explained in the PCT Application, the undercooled temperature of the liquid droplets upon impact with the substrate is critical to the formation of films and objects having desired properties. In some cases, where very small particles must be used in order to fabricate a desired type of object and the working distance must be a certain minimum distance in order to fabricate the object properly, conduction cooling causes the liquid droplets to cool too rapidly and to have an undesirable undercooled temperature upon impact with the substrate. Thus, there is a need for a way to reduce or eliminate contaminants and conduction cooling of the liquid droplets in the system described in the PCT Application.
In addition, the system described in the PCT Application does not include a device that can be used to direct the particles, and in turn the liquid droplets, toward a specific location on the substrate. Such a device is necessary in order to fabricate micro- and macro-scale objects having various shapes and sizes. Thus, there is also a need for a way to direct the particles and liquid droplets toward specific locations on the substrate.
What is needed, then, is a system and method for reducing or eliminating contamination and conduction cooling, and for directing particles and liquid droplets toward specific locations on a substrate.
Accordingly, one object is to provide a system and method for reducing or eliminating contaminants in particles and liquid droplets used to fabricate micro- and macro-scale objects.
Another object is to provide a system and method for reducing or eliminating conduction cooling of liquid droplets used to fabricate micro- and macro-scale objects.
Still another object of the present invention is to provide a system and method for directing particles and liquid droplets to specific locations on a substrate in order to fabricate micro- and macro-scale objects.
These and other objects are satisfied by a system enclosed in a vacuum chamber that includes a powder hopper, an enclosure containing a plurality of differentially pumped vacuum chambers, a tube, a charging lamp, a plurality of charging and heating diodes, and an electromagnetic steering device. The powder hopper is adapted to hold a plurality of metal or ceramic particles and the plurality of differentially pumped vacuum chambers are adapted to draw the particles out of the hopper and to propel the particles down the tube, which has one end connected to the enclosure and a second end pointing toward a substrate. The charging lamp is connected to the enclosure and is adapted to charge the particles as they pass through the enclosure. The charging and heating diodes are adapted to heat the particles as they pass through the tube. The electromagnetic field generating device is adapted to generate a steering magnetic field, which is used to direct the particles leaving the tube toward a specific location on the substrate. The electromagnetic field generating device can be adjusted to vary the magnetic field in order to direct the particles toward various locations on the substrate.
By enclosing the system in a vacuum, contaminants and conduction cooling are significantly reduced or eliminated. As an additional benefit, implementing the system in a vacuum allows the system to be used with other fabrication processes, such as vapor deposition processes, which are performed in a vacuum.